What Elements Make Up the Earth’s Atmosphere?
What is the Atmosphere?
Earth's atmosphere is a very thin layer of gases covering a very thin layer just above the surface of the planet. This layer of gases comprises a thickness of approximately 150 km (93 miles) and is held in place by the force of gravity. This layer is subsequently divided into five main layers: the troposphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere. Two of these gases exist in abundance, while the rest of the gases only exist in minimal amounts.
The atmosphere is divided into distinct layers according to a number of factors that vary greatly with height. Both air density and atmospheric pressure decrease uniformly with height. This causes the atmosphere to become thinner with increasing altitude. Atmospheric pressure maintains the vast majority of gases in the first 5.5 km (3.4 miles) above the Earth's surface. More than three-quarters of the gases that compose the atmosphere are contained within the troposphere, and it is also in this layer where the weather we experience takes place.
Air that is suitable for the process of photosynthesis is only found at the layer (troposphere) that is closer to the surface of the earth. The atmosphere protects the earth from incoming ultraviolet radiation and it also warms the planet by retaining heat.
Layers of the Atmosphere
The exosphere, which is the uppermost layer of the Earth’s atmosphere, is principally composed of the gases hydrogen and helium. These particles are widely spread apart and rarely collide with one another. The density is too low in the exosphere, making it easy for a particle to escape the Earth’s gravity. The exosphere is often considered as part of outer space, since there is not a clear boundary to its limits. The gases found in the exosphere include the lightest gases, such as hydrogen, helium, atomic oxygen, and carbon dioxide, which lie near the thermopause.
The thermosphere layer begins at approximately 85 km (53 miles). In this layer, temperatures can reach 1500 °C (2,700 °F) as a result of ultraviolet radiation absorption. Particles are widely spaced apart, and a molecule of oxygen may travel for about I km (0.62 miles) before impacting with other molecules.
The Hubble Space Telescope orbits the upper region of this layer at about 580 km (360 miles) of altitude. Space shuttles orbit in this layer, as well.
The color displays of auroras are produced in this layer, when charged particles from space collide with atoms and molecules exciting them into higher states of energy. When excited electrons return to their normal states, they emit photons of light, producing auroras at the poles.
The main components of the upper thermosphere include atomic oxygen, hydrogen, and helium.
The mesosphere extends from the stratopause, at 50 km (31 miles), to about 80-85 km (50-53 miles) in height. This is the layer where most meteors burn up when they enter the atmosphere. In the mesosphere, temperature decreases with altitude, and the temperature reaches its minimum at the mesopause at approximately -85 ° C (-120 ° F). At the very top of this layer, the condensation of crystals of water ice around frozen water vapor forms noctilucent clouds.
The stratosphere extends from around 11 km (6.8 miles) to about 50 km (31 miles). Most commercial air travel occurs in the lower section of the stratosphere. The temperature at the lower stratosphere remains cold -57 ° C; however, from the mid-region and up, the temperature increases with increasing altitude due to high ozone concentrations. Ozone concentrations absorb ultraviolet radiation, thus, protecting life on Earth. Atmospheric ozone, which is a reactive form of oxygen, is concentrated in a thin layer in the upper stratosphere at around 20-30 km (12-19 miles).
The troposphere, which is the lower layer of the atmosphere, occupies the first 11 km (6.8 miles) of the atmosphere, and contains 80% of the volume of the entire atmosphere. In the troposphere, the gases that compose the air we breathe are continuously circulating. In this layer the temperature decreases by about 6.4 ° C (14° F) per kilometer with increasing altitude. Most of the weather changes, including precipitation, temperature, wind and atmospheric pressure, occur in the troposphere. The elements composing the stratosphere are uniformly distributed with the exception of water vapor which exists in abundance at ground surface.
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Nitrogen, Oxygen and Traces of Other Gases
Composition of the Atmosphere
The thin layer surrounding the Earth that we know as atmosphere contains a mixture of gases. The most abundant gas is nitrogen, comprising 78%. The second most abundant gas is oxygen with 21%. Argon comprises 0.9% of the gas contents. Carbon dioxide abounds in about 0.039%. Helium, krypton, neon, hydrogen, xenon, among other gases exist in minor quantities. All these gases are held in the atmosphere by the force of gravity. It is in the troposphere where 80% of these gases abound, thus, making the troposphere a dense layer. Atmospheric pressure and air density decrease with altitude, therefore, the mixture of gases varies between layers.
The lower 75-100 km (46.5-62 miles) of the atmosphere is essentially uniform with a consistent ratio of gases from base to top. Above 100 km (62 miles), the distribution of nitrogen and oxygen, the denser gases, have become stable in the base, whereas lighter gases, including helium and hydrogen, have escaped even higher up. The upper portion of the atmosphere, known as the ionosphere, contains electrically charged particles known as ions. The ionosphere absorbs and reflects radio waves, influencing radio transmission and the formation of auroras at the poles.
Oxygen is utilized for respiration by most living organisms on earth. Nitrogen is converted by bacteria and lightning into ammonia and carbon dioxide is used by plants in the process of photosynthesis.
The atmosphere protects all living organisms on earth from the sun´s ultraviolet radiation and other high energetic particles-cosmic rays, solar wind, coming from space. The present composition of the earth´s atmosphere is the product of billions of years of biochemical modification by living organisms.
The following video shows the atmosphere from a real setting. The pilots are flying through the first two layers of the atmosphere. In the video, you will be able to watch the longest free fall ever attempted from over more than 30 km (19 miles) through the stratosphere and troposphere.
- Planets that have an atmosphere develop wind and weather
- Atmospheric pressure allows liquids to exist on a planet´s surface
- The Martian surface suggests that there was water on its surface in the past
- Without an atmosphere, a planet is bombarded by meteors creating crates on its surface
- Gases of low molecular weight are lost into space more than those of high molecular weight
- The friction created when a meteor enters a planet´s atmosphere causes it to burn before landing on a its surface
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© 2012 Jose Juan Gutierrez